1. Field of the Invention
The present invention relates to a power transmitting mechanism and a power transmitting method for switching over a transmission state of power from the driving side to the driven side.
2. Description of the Related Art
There is known a power transmitting mechanism, such as a clutch, for transmitting power generated by a power generating source, such as a motor, to a driven member.
Japanese Patent Laid-Open No. 2002-181072, for example, discloses a power transmission mechanism in which a flywheel is fixed to a rotary shaft of a power generating source and a center hub having a friction disk fitted to the hub is fixed to a rotary shaft of a driven member. The friction disk is brought into pressure contact with the flywheel through a spring arranged in a circumferential form, whereby torque generated from the power generating source is transmitted to the driven member with frictional force developed between the flywheel and the friction disk. The spring is supported by a cover, and a part of the spring on the outer peripheral side with respect to a supported portion presses the friction disk through a pressure plate. When a part of the spring on the inner peripheral side with respect to the supported portion is moved toward the flywheel, the part of the spring on the outer peripheral side with respect to the supported portion is moved away from the flywheel. Hence, the pressure contact between the friction disk and the flywheel is released and transmission of the torque is interrupted.
There is also known an electromagnetic clutch for switching over transmission and non-transmission of torque by using electromagnetic force. Japanese Patent Laid-Open No. 2002-048155, for example, discloses an electromagnetic clutch in which an output portion of a power generating source and a rotor are coupled to each other through a belt, and a hub rotating in union with an armature is fixed to a rotary shaft of a driven member. By exciting stator disposed inside the rotor having a C-shaped (or channel-like) section, the armature and the rotor are attracted to contact with each other, whereupon torque generated from the power generating source is transmitted to the driven member. By releasing the stator from the excited state, the electromagnetic force disappears and the armature and the rotor are separated from each other by spring force of a leaf spring member. Hence, transmission of the torque is interrupted.
However, those power transmission mechanisms have a limit in reducing the size because they require a large number of parts and have a complicated structure.
More specifically, the power transmitting mechanism as disclosed in Japanese Patent Laid-Open No. 2002-181072 requires a mechanical arrangement for moving the part of the spring on the inner peripheral side toward the flywheel when the clutch is decoupled, thus resulting in a complicated structure and a larger size.
In the power transmitting mechanism as disclosed in Japanese Patent Laid-Open No. 2002-048155, the clutch can be coupled by easily exciting the stator with energization of an electromagnetic coil contained inside the stator. However, problems arise in that response is poor because of attraction with excitation of the electromagnetic coil, and consumption of electricity is large because attraction force overcoming the load is required during transmission of power.